1. Field of the Invention
The invention relates to capacitors in integrated circuits and, in particular, to interdigitized capacitors with bent fingers.
2. Description of the Related Art
Capacitors are essential passive elements in integrated circuits for radio-frequency (RF) and mixed-signal applications such as filters, oscillators, analog to digital (A/D) converters, digital to analog (D/A) converters, and so on. Conventional capacitors such as horizontal parallel plate or metal-insulator-metal (MIM) structure are typically formed with two parallel plates separated by an interlevel dielectric (ILD) layer. However, in order to obtain high capacitance density, additional process steps are required to form thin dielectric, and cost is thus increased.
FIG. 1 shows a conventional interdigitized capacitor formed with interdigitized conductive lines. The alternating bias applied to interdigitized lines induces line to line coupling capacitance. High capacitance density can be achieved without additional process due to short distances between the interdigitized lines. Various interdigitized capacitors with multi-level stacked structures were have been developed. FIG. 2 is a schematic diagram of an exemplary interdigitized capacitor with parallel conductive lines and FIG. 3 a schematic diagram of a multi-layer capacitor structure with alternately connected concentric lines. However, most conventional technology provides limited capacitance density. In addition, structures thereof exhibit high series parasitic resistance due to long conductive lines, causing quality factor degradation, especially at high frequencies.
In mixed signal technologies, thick top metal layer are typically used to reduce metal loss such that quality factor is improved, with line-to-line spacing of the top metal layer accordingly higher than that of other metal layers. Accordingly, the top metal layer is not a good choice for an interdigitized array due to lower coupling efficiency compared with MIM capacitors.